createSTXPostCondition and createFungiblePostCondition allows to create invalid post conditions.

[LNow]

Both createSTXPostCondition and createFungiblePostCondition accepts values higher than 18446744073709551615 (max value of u64) and as a result they produce invalid post-conditions.

From https://github.com/stacksgov/sips/blob/main/sips/sip-005/sip-005-blocks-and-transactions.md

A STX post condition body is encoded as follows:

...
An 8-byte value encoding the literal number of microSTX

A Fungible token post-condition body is encoded as follows:

...
An 8-byte value encoding the literal number of token units

8-byte value (u64) not 16-byte value (u128)