Each REST API endpoint requires especially generated jwt(JSON Web Token). It should be passed as jwt get-parameter in each request. Here you can find the list of jwt libraries that supported by Atlassian and get the base idea around jwt .

Base domain:
https://cloudcrm.teamlead.ru/

Entities 
/entities (GET) - returns list of CRM entities including its tabs and fields (currently two entity types supported: 'company' and 'contact')

Query params: Not required

Entity Fields
/entityfields/company (GET) - returns existed company entity fields.
/entityfields/contact (GET) - returns existed contact entity fields.
 
Query params: Not required

Entity Tabs
/entitytabs/company (GET) - returns existed company entity tabs
/entitytabs/contact (GET) - returns existed contact entity tabs
Query params: Not required

Entity Rows
/entityrows (GET) - returns information about entity id and list of rows (including row data).

Query params:
entityId - identification number of entity.
page (optional) - numer of current page (pageSize parameter required).
pageSize(optional) - number of items to return per page (page parameter required).

Feild Types
/fieldtypes/company (GET) - returns list of field types for company entity.
/fieldtypes/contact (GET) - returns list of field types for contact entity.

Query params: Not required

To get API token please contact our support.