You need to specify activity in Top Object and child object and any number of optional parameters.

If you specify ob_name same as ob_top_name it will search for activity in Top Object

required parameters
(ob_top_id or ob_top_name) to specify Top Object (ob_id or ob_name) to specify child object and (a_id or a_name) to specify activity
optional parameters
new_a_name (new name for existing activity) a_date,a_duration, a_value,a_long_desc, a_label,a_bookmark,a_note, a_text1, a_text2, a_text3, a_text4, a_text5
response format
parameter reference

ob_top_id – Top Object id, unique

ob_name – Top Object name, not unique

ob_id – object id, unique

ob_name – object name, unique across project

a_name – name of activity, not unique

a_id – id of activity, unique

a_date – due date static set for activity in Catchr application

a_duration – due date dynamic, calculated from previous activity

a_bookmark – bookmark image

a_note – multiline note

a_long_desc – long description set in Catchr application

a_value – value of the activity, it can be 0 or 1 for check type activity, 0% or 25% or 50% or 75% or 100% for percent type activity, from 2 to 6 zeros or ones for flow type activity, eg. 00 – two stages, uncomplete, 111000 – six stages, three complete

a_label – label set for activity, label can be 0 to 5 comma separated, eg: 0,4,5 (first and last two)

a_seq_num – order id, lowest id is displayed at the top of the list

a_create_time – timestamp when activity was created

a_modify_time – timestamp when activity was last time modified

a_text1… a_text5 – text fields not used in Catchr application, but can be set and retrieved via REST API