It's possible to make a backup of only one/ones project from Jira Software Cloud?

[Jacobo Castro Ceballos]

We need to make a backup of one or more projects (Not all) from one cloud site to import to another cloud site, those sites belong to different customers.

Do you have any idea or any advice to do it?

We can not use any application assistance to migrate, because we are the owner of the new cloud site but we are not the owner of the first one. 

[Stefan Salzl]

As far as I know (needed that functionality too in the past) you can only do a backup of the whole site and not for seperate projects.

There is still an unresolved request regarding that you can vote for:

https://jira.atlassian.com/browse/JRACLOUD-60916

To keep your issues I would recommend to do an export of all issues of each project and import that into the new site. (which is still only an export and import. schemes, issue types, workflows etc would still needed to be configured manually)