Failed to fetch a free IP from proxy

Problem:

Hello! We are trying to set up Foreman in our company. We have the the following problem when we want to create a new host. When selecting domain and subnet we receive the following error:

Failed to fetch a free IP from proxy foreman-dev.xxx (https://foreman-dev.xxx:8443): ERF12-8202 [ProxyAPI::ProxyException]: Unable to retrieve unused IP ([RestClient::NotFound]: 404 Not Found) for proxy https://foreman-dev.xxx:8443/dhcp

When opening https://foreman-dev.xxx:8443/dhcp directly in the browser, I receive this message:

SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

Expected outcome:

Expcted outcome would be a suggested IP address

Foreman and Proxy versions:

Foreman 2.5.1

Foreman and Proxy plugin versions:

foreman_discovery 17.0.1

Distribution and version:

Debian 10, Buster

Other relevant data:

2021-07-21T11:26:12 [W|app|8ee1cee7] Failed to fetch a free IP from proxy foreman-dev.xxx (https://foreman-dev.xxx:8443): ERF12-8202 [ProxyAPI::ProxyException]: Unable to retrieve unused IP ([RestClient::NotFound]: 404 Not Found) for proxy https://foreman-dev.xxx:8443/dhcp: ERF12-8202 [ProxyAPI::ProxyException]: Unable to retrieve unused IP ([RestClient::NotFound]: 404 Not Found) for proxy https://foreman-dev.xxx:8443/dhcp

If smart proxy reports 404, it usually means the module was not enabled correctly. Even if you enabled DHCP module, during startup proxy might disable it due to error - e.g. cannot access dhcp server configuration etc. Check startup logs.

Mhm, thanks for the advice.
I found this messages in /var/log/foreman-proxy/proxy.log

2021-07-21T11:59:16 4cfa10f5 [I] Started GET /dhcp/213.xxx.xxx.xxx/unused_ip from=213.xxx.xxx.xxx&to=213.xxx.xxx.xxx
2021-07-21T11:59:16 4cfa10f5 [E] Subnet 213.xxx.xxx.xxx could not found
2021-07-21T11:59:16 4cfa10f5 [W] Error details for Subnet 213.xxx.xxx.xxx could not found: <Exception>: Subnet 213.xxx.xxx.xxx could not found
2021-07-21T11:59:16 4cfa10f5 [W] Subnet 213.xxx.xxx.xxxcould not found: <Exception>: Subnet 213.xxx.xxx.xxxcould not found
2021-07-21T11:59:16 4cfa10f5 [I] Finished GET /dhcp/213.xxx.xxx.xxx/unused_ip with 404 (3.74 ms)

Will investigate that further. Thank you.