def METHOD_NAME(legal_type: str):
    """Retrieve the next available sequential corp-num from Lear or fallback to COLIN."""
    # this gets called if the new services are generating the Business.identifier.
    if legal_type in BusinessType:
        if business_type := BusinessType.get_enum_by_value(legal_type):
            return BusinessIdentifier.next_identifier(business_type)
        return None
    # legacy Business.Identifier generation
    try:
        # TODO: update this to grab the legal 'class' after legal classes have been defined in lear
        if legal_type in (Business.LegalTypes.BCOMP.value,
                          Business.LegalTypes.BC_ULC_COMPANY.value,
                          Business.LegalTypes.BC_CCC.value,
                          Business.LegalTypes.COMP.value):
            business_type = 'BC'
        else:
            business_type = legal_type
        token = AccountService.get_bearer_token()
        resp = requests.post(
            f'{current_app.config["COLIN_API"]}/{business_type}',
            headers={**AccountService.CONTENT_TYPE_JSON,
                     'Authorization': AccountService.BEARER + token}
        )
    except requests.exceptions.ConnectionError:
        current_app.logger.error(f'Failed to connect to {current_app.config["COLIN_API"]}')
        return None
    if resp.status_code == 200:
        new_corpnum = int(resp.json()['corpNum'])
        if new_corpnum and new_corpnum <= 9999999:
            # TODO: Fix endpoint
            return f'{business_type}{new_corpnum:07d}'
    return None