Steps to Reproduce the Bug

I can't log into my fabric 1.21 server "Internal Exception: io.netty.handler.codec.EncoderExeption: Failed to encode packet 'clientbound/minecraft:custom_payload' (spawnermod:packet.sync_config_message)"

Enhanced Mob Spawner filename

spawnermod-1.21.1-1.2.6+Fabric

Other mod filename (Optional)

animatica 0.6.1+1.21 - architectury 13.0.6 - asteroid 0.2.0 - auto-workstations 1.0-rc.25 - bettermounthud 1.2.4 - capes 1.5.4+1.21 - carpet 1.4.147+v240613 - carpet-extra 1.4.147 - cicada 0.8.3+1.21-and-above - cloth-config 15.0.128 -- cloth-basic-math 0.6.1 - collective 7.81 - continuity 3.0.0-beta.5+1.21 - controlify 2.0.0-beta.14+1.21-fabric |-- dev_isxander_libsdl4j 3.6896c4c-38 |-- org_hid4java_hid4java 0.7.0 |-- org_quiltmc_parsers_gson 0.3.0 -- org_quiltmc_parsers_json 0.3.0 - copperhopper 0.9.3+1.21 - cubes-without-borders 2.1.1+1.21 - customspeed 2.0.2-1.21 - debugify 1.21+1.0 - dynamic_fps 3.6.3 -- net_lostluma_battery 1.1.0 - e4mc_minecraft 5.1.0 -- folk_sisby_kaleido-config 0.3.1+1.3.1 - easyvillagertrade 1.2.1-1.21 - enchant-tooltips 1.0.1 - enhancedblockentities 0.10.1+1.21 - entity_model_features 2.1.3 - entity_texture_features 6.1.3 -- org_apache_httpcomponents_httpmime 4.5.10 - entityculling 1.6.6 - expandedstorage 14.0.2 - fabric-api 0.100.8+1.21 |-- fabric-api-base 0.4.42+6573ed8cd1 |-- fabric-api-lookup-api-v1 1.6.67+b5597344d1 |-- fabric-biome-api-v1 13.0.29+5bd9f1bcd1 |-- fabric-block-api-v1 1.0.22+0af3f5a7d1 |-- fabric-block-view-api-v2 1.0.10+6573ed8cd1 |-- fabric-blockrenderlayer-v1 1.1.52+0af3f5a7d1 |-- fabric-client-tags-api-v1 1.1.15+6573ed8cd1 |-- fabric-command-api-v1 1.2.49+f71b366fd1 |-- fabric-command-api-v2 2.2.28+6ced4dd9d1 |-- fabric-commands-v0 0.2.66+df3654b3d1 |-- fabric-content-registries-v0 8.0.15+b5597344d1 |-- fabric-convention-tags-v1 2.0.18+7f945d5bd1 |-- fabric-convention-tags-v2 2.4.2+c111832ad1 |-- fabric-crash-report-info-v1 0.2.29+0af3f5a7d1 |-- fabric-data-attachment-api-v1 1.1.25+6a6dfa19d1 |-- fabric-data-generation-api-v1 20.2.13+16c4ae25d1 |-- fabric-dimensions-v1 4.0.0+6fc22b99d1 |-- fabric-entity-events-v1 1.6.12+6fc22b99d1 |-- fabric-events-interaction-v0 0.7.10+e633f883d1 |-- fabric-game-rule-api-v1 1.0.53+6ced4dd9d1 |-- fabric-item-api-v1 11.0.0+afdfc921d1 |-- fabric-item-group-api-v1 4.1.3+78017270d1 |-- fabric-key-binding-api-v1 1.0.47+0af3f5a7d1 |-- fabric-keybindings-v0 0.2.45+df3654b3d1 |-- fabric-loot-api-v2 3.0.13+3f89f5a5d1 |-- fabric-loot-api-v3 1.0.1+3f89f5a5d1 |-- fabric-message-api-v1 6.0.13+6573ed8cd1 |-- fabric-model-loading-api-v1 2.0.0+fe474d6bd1 |-- fabric-object-builder-api-v1 15.1.13+d1321076d1 |-- fabric-particles-v1 4.0.2+6573ed8cd1 |-- fabric-recipe-api-v1 5.0.10+65089712d1 |-- fabric-registry-sync-v0 5.0.26+a5d66753d1 |-- fabric-renderer-api-v1 3.3.0+0ae0b97dd1 |-- fabric-renderer-indigo 1.6.5+48fb1586d1 |-- fabric-renderer-registries-v1 3.2.68+df3654b3d1 |-- fabric-rendering-data-attachment-v1 0.3.48+73761d2ed1 |-- fabric-rendering-fluids-v1 3.1.6+b5597344d1 |-- fabric-rendering-v0 1.1.71+df3654b3d1 |-- fabric-rendering-v1 5.0.5+df16efd0d1 |-- fabric-resource-conditions-api-v1 4.2.1+d153f344d1 |-- fabric-screen-api-v1 2.0.24+b5597344d1 |-- fabric-screen-handler-api-v1 1.3.83+b5597344d1 |-- fabric-sound-api-v1 1.0.23+6573ed8cd1 |-- fabric-transfer-api-v1 5.1.15+3dccd343d1 -- fabric-transitive-access-wideners-v1 6.0.12+6573ed8cd1 - fabric-language-kotlin 1.11.0+kotlin.2.0.0 |-- org_jetbrains_kotlin_kotlin-reflect 2.0.0 |-- org_jetbrains_kotlin_kotlin-stdlib 2.0.0 |-- org_jetbrains_kotlin_kotlin-stdlib-jdk7 2.0.0 |-- org_jetbrains_kotlin_kotlin-stdlib-jdk8 2.0.0 |-- org_jetbrains_kotlinx_atomicfu-jvm 0.24.0 |-- org_jetbrains_kotlinx_kotlinx-coroutines-core-jvm 1.8.1 |-- org_jetbrains_kotlinx_kotlinx-coroutines-jdk8 1.8.1 |-- org_jetbrains_kotlinx_kotlinx-datetime-jvm 0.6.0 |-- org_jetbrains_kotlinx_kotlinx-serialization-cbor-jvm 1.6.3 |-- org_jetbrains_kotlinx_kotlinx-serialization-core-jvm 1.6.3 -- org_jetbrains_kotlinx_kotlinx-serialization-json-jvm 1.6.3 - fabricloader 0.15.11 -- mixinextras 0.3.5 - fabricskyboxes 0.7.4+mc1.21 - fabrishot 1.14.0 - fastquit 3.0.0+1.20.6 - fasttrading 0.1.5+1.21 - ferritecore 7.0.0 - fsb-interop 1.4.0+mc1.21-build.54 - g4mespeed 1.4.6-mc1.21 -- g4mespeed-ui 0.9.10-mc1.21 - gammautils 1.9.20 - growmeal-fabric 1.2.1 - hopperhedgehog 2.1.0-1.20.5 - immediatelyfast 1.2.18+1.21 -- net_lenni0451_reflect 1.3.4 - indium 1.0.34+mc1.21 - infinitetrading 4.5 - inventive_inventory 0.4.6 - iris 1.7.3+mc1.21 |-- io_github_douira_glsl-transformer 2.0.1 |-- org_anarres_jcpp 1.4.14 -- org_antlr_antlr4-runtime 4.13.1 - isxander-main-menu-credits 1.2.0 - jade 15.1.5+fabric - java 21 - languagereload 1.6.1+1.21 - litematica 0.18.999-sakura.4 - lithium 0.12.7 - malilib 0.19.999-sakura.2 - minecraft 1.21 - mixintrace 1.1.1+1.17 - modelfix 1.21-1.6 - modernfix 5.19.0+mc1.21 - modmenu 11.0.1 -- placeholder-api 2.4.0-pre.2+1.21 - moreculling 0.26.0 |-- com_github_fallen-breath_conditional-mixin v0.6.2 -- mixinsquared 0.1.1 - mousetweaks 2.26 - nochatreports 1.21-v2.8.0 - offershud 1.21-1.6.1 - omnihopper 2.3.2+1.21 -- cooldown-coordinator 0.7.2 - optigui 2.3.0-beta.2+1.21 |-- org_apache_commons_commons-text 1.12.0 -- org_ini4j_ini4j 0.5.4 - owo 0.12.11+1.21 |-- io_wispforest_endec 0.1.5 |-- io_wispforest_endec_gson 0.1.3 |-- io_wispforest_endec_jankson 0.1.3 -- io_wispforest_endec_netty 0.1.2 - paginatedadvancements 2.4.2 - polytone 1.21-2.2.10 -- net_objecthunter_exp4j 0.4.8 - puzzle 1.6.3+1.21 |-- midnightlib 1.5.7 |-- puzzle-base 1.6.3+1.21 |-- puzzle-gui 1.6.3+1.21 |-- puzzle-models 1.6.3+1.21 -- puzzle-splashscreen 1.6.3+1.21 - quickcurefabricrewrite 1.0.1-1.21 - reeses-sodium-options 1.7.3+mc1.21 - resourcify 1.4.0 -- universalcraft 342 - roughlyenoughitems 16.0.744 -- error_notifier 1.0.9 - rrls 5.0.1+mc1.21-fabric - scroll-for-worldedit 1.1.4 - shulkerboxtooltip 5.0.4+1.21 - silk-all 1.10.7 |-- silk-commands 1.10.7 |-- silk-core 1.10.7 |-- silk-game 1.10.7 |-- silk-igui 1.10.7 |-- silk-nbt 1.10.7 |-- silk-network 1.10.7 -- silk-persistence 1.10.7 - smelterhedgehog 1.1.0-1.21 - sodium 0.5.11+mc1.21 - sodium-extra 0.5.7+mc1.21 -- caffeineconfig 1.3.0+1.17 - spawnermod 1.2.6 - squatgrow 21.0.3+mc1.21 - stack-to-nearby-chests 0.5.8 -- libgui 11.0.0+1.21 |-- jankson 8.0.0+j1.2.3 | -- blue_endless_jankson 1.2.3 -- libninepatch 1.2.0 - toms_storage 2.0.9 |-- cardinal-components-base 6.1.0 -- cardinal-components-block 6.1.0 - trade_cycling 1.21.1-1.0.13 |-- fabric-lifecycle-events-v1 2.3.12+6c1df3606a |-- fabric-networking-api-v1 4.2.2+60c3209b6a -- fabric-resource-loader-v0 1.3.0+565991296a - treeharvester 9.0 - tweakermore 3.19.0 |-- conditional-mixin 0.6.2 -- mixinextras 0.3.5 - tweakeroo 0.20.999-sakura.3 - veinminer 2.1.2 -- de_miraculixx_core 2.1.2 - villager-pickup 1.1.2 - visibletraders 0.0.3 - worldedit 7.3.6+6892-3d660b8 - xaerominimap 24.2.1 - xaeroworldmap 1.38.8 - yet_another_config_lib_v3 3.5.0+1.21-fabric

Extra Notes (Optional)

I put all the mods I have, help :C

Thanks for the report, I will look into this.

At the moment this mod is not compatible with servers until this issue is fixed.

The issue is fixed and here's a link to updated file https://modrinth.com/mod/enhanced-mob-spawners/version/1.2.7