Uniprot identifiers are not recognized

When uploading a list of proteins a fraction of the identifiers are not recognized. specifically those that have this format C1BPY5, C1BQN9, C1BPZ3, C1BQ63, C1BMW4, C1BP73, C1BRU1, C1BNG7, etc.
I try to convert them with the tool available on the page and it is not possible.
Any suggestions?
The identifiers were obtained from UniprotKB, and correspond to the species caligus rogercresseyi

Thanks in advance for any help!