Problem with access of the Fiori-Launchpad (S4HANA-1909 - CAL Instance)

We are having a problem with access of the Fiori-Launchpad of our S4HANA-1909 CAL Instance:

https://vhcals4hcs.dummy.nodomain:44301/sap/bc/ui5_ui5/ui2/ushell/shells/abap/FioriLaunchpad.html#Shell-home

Error:503 Service Not Available. SSL peer certificate untrusted

Under smicm:

[Thr 139857196750592] *** ERROR during secussl_read() from SSL_read()==SSL_ERROR_SSL [Thr 139857196750592] cli SSL session PSE "/usr/sap/S4H/D00/sec/SAPSSLS.pse" [Thr 139857196750592] session ciphersuites=150:PFS:HIGH::EC_P256:EC_HIGH [Thr 139857196750592] Client SSL_CTX 7f3302f27260 pvflags=896 (TLSv1.2,TLSv1.1,TLSv1.0) [Thr 139857196750592] TLSextSNI server_name="vhcals4hcs.dummy.nodomain" [Thr 139857196750592] secussl_read: SSL_read() failed (536872221/0x2000051d) [Thr 139857196750592] => "Failed to verify peer certificate. Peer not trusted." [Thr 139857196750592] Thu Jul 2 11:14:06:897 2020 [Thr 139857196750592] >> Begin of Secu-SSL Errorstack >> [Thr 139857196750592] 0x2000051d SAPCRYPTOLIB SSL_read [Thr 139857196750592] SSL API error [Thr 139857196750592] Failed to verify peer certificate. Peer not trusted. [Thr 139857196750592] 0xa0600203 SSL ssl3_read_bytes [Thr 139857196750592] Peer not trusted [Thr 139857196750592] 0xa0600203 SSL ssl3_connect [Thr 139857196750592] Peer not trusted [Thr 139857196750592] 0xa0600203 SSL ssl3_get_server_certificate [Thr 139857196750592] Peer not trusted [Thr 139857196750592] 0xa0600203 SSL ssl3_decode_server_certificate [Thr 139857196750592] Peer not trusted [Thr 139857196750592] 0xa0600203 SSL ssl_verify_peer_certificates [Thr 139857196750592] Peer not trusted [Thr 139857196750592] 0xa0600203 SSL ssl_cert_checker_verify_certificates [Thr 139857196750592] Peer not trusted [Thr 139857196750592] 0xa0600203 SSL ssl_cert_checker_verify_certificates [Thr 139857196750592] Peer not trusted [Thr 139857196750592] Certificate: [Thr 139857196750592] Certificate: [Thr 139857196750592] Subject: CN=vhcals4hcs.dummy.nodomain, OU=S4H, O=SAP Trust Community, C=DE [Thr 139857196750592] Issuer: CN=cal.dummy.nodomain, OU=S4H, O=SAP, C=DE [Thr 139857196750592] Serial Number: 10:08 [Thr 139857196750592] Verification result: [Thr 139857196750592] Status: Not successful [Thr 139857196750592] SignerStatus: Not successful [Thr 139857196750592] SignerVerificationResult: None [Thr 139857196750592] << End of Secu-SSL Errorstack [Thr 139857196750592] (No certificate request received from Server) [Thr 139857196750592] Target Hostname="vhcals4hcs.dummy.nodomain" [Thr 139857196750592] SSL NI-hdl 137: local=10.0.2.236:60148 peer=10.0.2.236:44301 [Thr 139857196750592] <<- ERROR: SapSSLSessionStartNB(sssl_hdl=7f32e0001610)==SSSLERR_PEER_CERT_UNTRUSTED