App Router Issue: Cookies() doesn't run inside a Server Action

import { cookies } from 'next/headers'

export const getTokens = async (code: string): Promise<string> => {
    'use server'
    console.log('\n entering SERVER ACTION: getTokens(code) . . .\n');
    const envIntegrationKey = process.env.NEXT_PUBLIC_DOCUSIGN_INTEGRATION_KEY
    const envSecretKey = process.env.DOCUSIGN_SECRET_KEY



    const tokenURI = 'https://account-d.docusign.com/oauth/token/';
    const credentials = btoa(

);

    
    const reqBody = new URLSearchParams();
    reqBody.append('grant_type', 'authorization_code');
    reqBody.append('code', code);

    const response = await fetch(tokenURI, {
        method: 'POST',
        headers:{
            Authorization: 

        },
        body: reqBody
    })

    
    if (response.ok) {
        console.log('response OK: ', response.status, 'Status Text: ', response.statusText);
        const data = await response.json()
        const accessToken: string = data.access_token;
        const refreshToken: string = data.refresh_token; 
        const expiresIn: string = data.expires_in.toString();

        cookies().set('accessToken', accessToken)
        cookies().set('refreshToken', refreshToken)

//rest of code