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The 200 listeners limitation (up to 100 active listeners) for Application Gateway is a hard limit and cannot be increased.
The work around in the scenario will be to
- Create another application gateway instance and divide the listeners.
OR - The other work around in this case will be migrate to application gateway v2 SKU and use the Wildcard host names in listener to reduce the number of listeners. Use of this functionality will again depend on your set-up and the domains hosted on your application gateway.
Hope this helps! Please let me know if you have any additional questions. Thank you!