You must send in Space Ape Club apes with Space Ape Club serums. The number of serums in a transaction must be the same as the number of apes being sent in.
All apes being sent in must be unmutated.
For each ape/serum, there must also be a payment of either
10 ADA + 400 $SACT or 60 ADA
You can send in up to 10 apes in each transaction. If any apes have already been mutated or if the payment in invalid, the transaction will be refunded. For every Extreme Serum you use, you will get back an Extreme Mutated Ape in addition to the normal Radioactive Mutated Ape
You can use the Mutation Checker to determine if an Ape has already been mutated:here