public Mono<ResponseStatusCode> isAllowedToBeInvited(
            @NotNull Long groupId,
            @NotNull Long inviteeId) {
        return isGroupMember(groupId, inviteeId, false).flatMap(isGroupMember -> {
            if (isGroupMember) {
                return Mono.just(ResponseStatusCode.SEND_GROUP_INVITATION_TO_GROUP_MEMBER);
            }
            return groupBlocklistService.isBlocked(groupId, inviteeId)
                    .map(isBlocked -> isBlocked
                            ? ResponseStatusCode.SEND_GROUP_INVITATION_TO_BLOCKED_USER
                            : ResponseStatusCode.OK);
        });
    }
@return Possible codes: {@link ResponseStatusCode#OK},
        {@link ResponseStatusCode#SEND_GROUP_INVITATION_TO_GROUP_MEMBER},
        {@link ResponseStatusCode#SEND_GROUP_INVITATION_TO_BLOCKED_USER}
turms-service/src/main/java/im/turms/service/domain/group/service/GroupMemberService.java