How about the following suggestions?

Suggestion 1:

Modify fields in your request body as follows:

From:

fields: '*',

To:

fields: 'effectiveValue,effectiveFormat',

Suggestion 2:

Modify fields, effectiveValue and effectiveFormat in your request body as follows. (effectiveValue and effectiveFormat are modified to userEnteredValue and userEnteredFormat, respectively.)

From:

fields: '*',
rows: [
    {
        values: [
            {
                effectiveValue: {
                    stringValue: 'hello please',
                },
                effectiveFormat: {

To:

fields: 'userEnteredValue,userEnteredFormat"',
rows: [
    {
        values: [
            {
                userEnteredValue: {
                    stringValue: 'hello please',
                },
                userEnteredFormat: {

Reference:

• UpdateCellsRequest