How do I fix 'Cannot join' error in shared albums on iPhone?

Re: "Shared Albums Issue"

"... when I send shared albums, the people who I invited cannot see my invites"

You may want to check that:

• you are providing the iCloud storage space for the albums you want to share

and

• that those you want to share with know that they can view pending invitations,

ie: by tapping "Collections", then tapping their Apple Account profile."

Create shared albums in Photos on iPhone - Apple Support

Eg" says:

"To invite people to join the shared album,

see Add and remove people in a shared album.

Note: The organizer of a shared album provides the iCloud storage space for its content. Albums set to expire don’t use any iCloud storage."

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Re: "When I try to join it says "Cannot join ..." as an error message"

Above linked article also says:

"Join a shared album

Select the link you received, then select Join.

You may need to ask for access, provide your email, or sign in to your Apple Account.

If you join by email and want to save the album to your account, select Join, then sign in to your Apple Account.

To view pending invitations, tap Collections, then tap your Apple Account profile."

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More info if needed: Trouble-shooting tips:

See what to do: If you can't see your shared album - Apple Support

and

Others have encountered difficulties too:

Eg: See this other discussion thread:

Cannot join Photos Shared Albums - Apple Community