Hey to complete what mrstorax just said I'd add that, I did some tests to include a struct composed with a struct of traits and the metadata link in attributes field when minting nfts. The goal is to have access to attributes on chain and to allow the api to display the metadata file (to display attributes correctly in marketplaces).
All this to say that until a few days ago the api (on devnet at least) could trim everything before "metadata:" in the attributes field to allow marketplaces to retrieve the metadata correctly. And now it doesn't work on the mainnet, do you have any idea why and solutions to suggest?
to illustrate, I use this struct in the attributes field