Hello 
I have a problem with DOI registration in one of the journals. DOI numbers from 1 to 5 can be registered, but it is impossible with further numbers . I get the information that “The given DOI suffix is already in use for another published item. Please enter a unique DOI suffix for each item.” The DOIs haven’t been registered - I confirmed it with CrossRef. I have no idea what the problem may be.
Please help:))
The DOI prefix is used as a namespace so that DOIs are globally unique without requiring global coordination for every new identifier. Each organisation is assigned its own unique prefix, and given rights to decides its own suffix format.
The most important property of a DOI suffix is that it should be unique within the given prefix space.
If you get the information that “The given DOI suffix is already in use for another published item. Please enter a unique DOI suffix for each item.”
The only chance is you may use that suffix already.
Please check with the numbers you have entered (or) Contact your service provider (CrossRef).
I confirmed with Crossref that none of the DOI numbers in question have been registered:(