What configuration of the add-on have you done?
According to https://splunkbase.splunk.com/app/3703/#/details, you need to have Chat & Bot IDs (ref: https://core.telegram.org/bots/api)
Do you have them?
from User warren – Stack Overflow https://stackoverflow.com/questions/69895159/splunk-issue-with-telegram-alert-action-can-not-configure-the-action-splunk-ent/69898858#69898858
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