No IPV6 Adress from ISP via EG-25G LTE Modem?

[maxgeb]

IPv4 works perfectly,  but dhcpv6 ends with:

2021-07-24T14:03:22   ppp[29715]   [opt2]   IPV6CP:   parameter   negotiation   failed                  
2021-07-24T14:03:20   ppp[29715]   [opt2]   IPV6CP:   SendConfigReq   #10                     
2021-07-24T14:03:18   ppp[29715]   [opt2]   IPV6CP:   SendConfigReq   #9         

Do i have to stick with IPv4 or can i do something about that?

[bartjsmit]

Do i have to stick with IPv4 or can i do something about that?

Plenty stuff still to tinker with in Interfaces, WAN:
IPv6 Configuration Type: DHCPv6, Track Interface or SLAAC

You should get connected by going through all the options under Basic (prefix request, size, hint and use IPv4). Your ISP will know your prefix size, so only 24 different combinations to try 

Bart...