openvpn client on owrt without .ovpn

[lm2lm2]

hello

im trying to connect my router openwrt as a openvpn client, without .ovpn file
unfortunately, i get :
daemon.warn openvpn(custom_config)[775]: Cannot load private key file /etc/openvpn/key: error:0906D06C:lib(9):func(109):reason(108): error:140B0009:lib(20):func(176):reason(9)


my provider is proton, i have as follow :
cacert.pem certificate from proton
key as the id/password, on two lines, of credentials for vpn
this :
(ca)
-----BEGIN CERTIFICATE-----
XXX..
-----END CERTIFICATE-----

and this :
<tls-crypt>
-----BEGIN OpenVPN Static key V1-----
-----END OpenVPN Static key V1-----

but it's failing on :

daemon.warn openvpn(custom_config)[775]: Cannot load private key file /etc/openvpn/key: error:0906D06C:lib(9):func(109):reason(108): error:140B0009:lib(20):func(176):reason(9)

how could i solve it?
thank you vm!