Error after logging in to the Magento Admin

The requested URL /magento2index.php/admin/admin/dashboard/index/key/0c81957145a968b697c32a846598dc2e/ was not found on this server.

Note the lack of a slash character between magento2 and index.php in the URL.

The base URL is not correct. The base URL must:

Start with http:// or https://
End with a slash (/)
Match the case of the web/unsecure/base_url record in the core_config_data database table

Re-run the installation using a valid value.