When changing the external database password via the vAPP console you may find that some special characters are not accepted.
vAPP does not allow the following characters in the external DB password:
# at the beginning
The rest of the constraints, if any, are imposed are by the DB.
Also, note that you must apply the latest patches of 14.2/14.3 which fix an issue where some special characters were not allowed in the DB password.
For 14.2 apply vAPP CP05 or higher, for 14.3 apply vAPP CP01 or higher.