guys I am running into "We couldn't find this contract. Please ensure that this is a valid ERC721 or ERC1155 contract deployed on Rinkeby and that you have already minted items on the contract."
when trying to import an erc1155 on Opensea, any ideas on what might be the cause/ how to solve?

If it's relevant I did not mint tokens in the constructor but I did that in a second moment, and from the ERC1155 standard:
"Smart contracts implementing the ERC-1155 standard MUST implement all of the functions in the ERC1155 interface.

Smart contracts implementing the ERC-1155 standard MUST implement the ERC-165 supportsInterface function and MUST return the constant value true if 0xd9b67a26 is passed through the interfaceID argument."

both these conditions are true