A subscription is based on a Virtuozzo Container type hosting plan that has a non-zero Number of databases (numdbs) included. Can the subscription hosting plan be changed to a hosting plan with Number of databases (numdbs) included amount set as "0 of 0 database(s)"?
The feature request PBAS-20526 to make it possible to set the number of databases billable resource as unlimited was implemented in OBAS 4.5.7 release.
To support unlimited Number of databases (numdbs), please upgrade to 4.5.7 as described in How to upgrade OBAS system to the latest available version.
Workaround for 4.5.6 and older versions
Workaround is to modify numdbs in the target plan to be compliant with the source one.
An alternative solution is to drop databases of the Container in question.
WARNING Please make sure that the databases do not contain any valuable data prior to deleting them.