Regalium Ingot has the tags

• minecraft:beacon_payment_items
• forge:ingots
• forge:ingots/regalium
• and: forge:nuggets/regalium

the regalium nugget just has the forge:nuggets tag, altough it should also have forge:nuggets/regalium, which the ingot currently has
Mc-version: 1.16.5
Forge: 36.0.13
Undergarden: 1.16.5-0.4.5