Send Post Request to Swym in Remix Action

Question

I have a form that I'd like to send a POST request to Swym to set up back in stock alerts. I'm using Shopify's Hydrogen framework, which is built with Remix. Right now I have an action that is calling my POST function, but I keep getting errors and the page stops working. Am I setting this up correctly?

Here is my action, form, and function to call API:

export const action = async ({request}: ActionArgs) => {
  const formData = await request.formData();
  const userEmail = formData.get('email');
  const productId = formData.get('productId');
  const productVariantId = formData.get('productVariantId');
  const productUrl = formData.get('productUrl');

  getSwym(userEmail, productId, productVariantId, productUrl);
  return json({message: 'getSwym has run'}, {formData: formData});
};

export async function getSwym(
  userEmail: string | null,
  productVariantId: string | null,
  productId: string | null,
  productUrl: string | null,
) {

  const endpoint = `https://swymstore-v3premium-01.swymrelay.com/storeadmin/bispa/subscriptions/create`;

  const API_KEY = btoa(
    '{API KEY}',
  );
  const PID = btoa('{API KEY}');

  const requestOptions = {
    method: 'POST',
    headers: {
      Accept: 'application/json',
      'Content-Type': 'application/x-www-form-urlencoded',
      Authorization: `Basic ${API_KEY} : ${PID}`,
    },
    body: new URLSearchParams({
      products: [
        {
          // 'PRODUCT VARIANT ID'
          epi: productVariantId,
          // 'PRODUCT ID/PRODUCT MASTER ID'
          empi: productId,
          // 'CANNONICAL URL OF THE PRODUCT'
          du: `http://localhost:3000/products/${productUrl}`,
        },
      ],
      medium: 'email',
      mediumvalue: `${userEmail}`,
      topics: ['backinstock', 'comingsoon'],
      addtomailinglist: '1',
      prototype: null,
      toString: () => {
        throw new Error('Not yet implemented!');
      },
    }).toString(),
  };

  const response = await fetch(endpoint, requestOptions);
  const data = await response.json();

  return data;
}