One of the biggest problems with self employed sponsors, is confusion about how to state their income. People who are NOT self employed also get confused about this and confuse "revenue" with "income". In this context the self employed sponsor's current income is exactly the number on the "Total Income" titled line of their most recent 1040. In this case, that is presumably from 2023.
If the total income (in this case it's pretty important it be all three years) is well above the minimum, income requirement, then there's no big issue. Even better would be to use an Tax Return Transcript, but still the number comes from the total income line.
If the joint sponsor is married, provide an I-864a from their spouse, even if the spouse has no income.
You will also need evidence they are currently living in the USA, like a utility bill, etc.