Hello @Danilo Ortiz , Thank you for providing additional details. Can you try below mentioned steps and see if that resolves the issue.
- Can you try clearing cookies and cache for your browser and see if issue persists? Can you also try using a different browser?
- Can you try deploying the application gateway resource using Azure PowerShell or using Azure CLI ? and use the existing Virtual Networks, please let me know if you get any errors which might give us more insights. If the error is regarding permission required can you check your Azure Role Assignment as mentioned in the next step. Also please make sure that these virtual networks have a dedicated subnet for Application Gateway. Please go through this documentation for Virtual network requirements and Subnet Size.
- Can you check what Azure role assignment you have for your subscription or the resource groups listed above? I think you at least need to have Virtual Machine Contributor role in order to add Application Gateway/ Azure Load balancer backend pool. You can also explore some additional roles and see any other roles suits your requirements. Please let me know if you any additional concerns here.
- Lastly these are the NSG requirements for Application gateway, can you please validate them for your Virtual Networks and see if any are missing?
I hope this helps. Please let me know if the issue still persists. Thank you!