Being very concerned, outsiders terminated payment in St Petersburg, for instance (8)
I believe the answer is:
troubled
'being very' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I can't see?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for troubled that I've seen before include "Distressed, perturbed" , "Bothered, perturbed" , "Bothered, disquieted" , "Inconvenienced" , "Caused distress to" .)