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Spine appends numbers to make the names unique when required for the skeleton's uniqueness rules. If you move all your attachments under the same slot, then rename them (select them all, F2), Spine will give them each a unique numeric suffix.

That solved my problem thank you!

Is there any possible way to rename all the attachment names with sequential numbers at the same time in Spine? ( a1 - a2 - a3...). I've tried to rename them by selecting all and use F2, but instead of different numbers I get the same number and name on all the attachments.