code: @Nullable
      public Token createAccountTokenSynchronous(
              @NonNull final AccountParams accountParams,
              @Nullable String publishableKey)
              throws AuthenticationException,
              InvalidRequestException,
              APIConnectionException,
              APIException {
          String apiKey = publishableKey == null ? mDefaultPublishableKey : publishableKey;
          if (apiKey == null) {
              return null;
          }
          validateKey(publishableKey);
          RequestOptions requestOptions = RequestOptions.builder(
                  publishableKey, mStripeAccount, RequestOptions.TYPE_QUERY)
                  .build();
          try {
              return mApiHandler.createToken(
                      accountParams.toParamMap(),
                      requestOptions,
                      Token.TYPE_ACCOUNT
              );
          } catch (CardException exception) {
              // Should never occur. CardException is only for card related requests.
          }
          return null;
      }
docs: Blocking method to create a {@link Token} for a Connect Account. Do not call this on the UI
  thread.
  
  @param accountParams params to use for this token.
  @param publishableKey the publishable key to use with this request. If null is passed in as
  the publishable key, we will use the default publishable key.
  @return a {@link Token} that can be used for this account.
  
  @throws AuthenticationException failure to properly authenticate yourself (check your key)
  @throws InvalidRequestException your request has invalid parameters
  @throws APIConnectionException failure to connect to Stripe's API
  @throws APIException any other type of problem (for instance, a temporary issue with
  Stripe's servers)