diff --git a/authorization.go b/authorization.go
index 361f6a0..96a2eb8 100644
--- a/authorization.go
+++ b/authorization.go
@@ -27,7 +27,7 @@ func (c *Client) GetAuthorization(authID string) (*Authorization, error) {
 func (c *Client) CaptureAuthorization(authID string, a *Amount, isFinalCapture bool) (*Capture, error) {
 	isFinalStr := strconv.FormatBool(isFinalCapture)
 
-	buf := bytes.NewBuffer([]byte("{\"amount\":{\"currency\":\"" + a.Currency + "\",\"total\":\"" + a.Total + "\"},\"is_final_capture\":" + isFinalStr + "}"))
+	buf := bytes.NewBuffer([]byte(`{"amount":{"currency":"` + a.Currency + `,"total":"` + a.Total + `"},"is_final_capture":` + isFinalStr + `}`))
 	req, err := http.NewRequest("POST", fmt.Sprintf("%s%s", c.APIBase, "/v1/payments/authorization/"+authID+"/capture"), buf)
 	if err != nil {
 		return &Capture{}, err
@@ -56,7 +56,7 @@ func (c *Client) VoidAuthorization(authID string) (*Authorization, error) {
 // PayPal recommends to reauthorize payment after ~3 days
 // Endpoint: POST /v1/payments/authorization/ID/reauthorize
 func (c *Client) ReauthorizeAuthorization(authID string, a *Amount) (*Authorization, error) {
-	buf := bytes.NewBuffer([]byte("{\"amount\":{\"currency\":\"" + a.Currency + "\",\"total\":\"" + a.Total + "\"}}"))
+	buf := bytes.NewBuffer([]byte(`{"amount":{"currency":"` + a.Currency + `","total":"` + a.Total + `"}}`))
 	req, err := http.NewRequest("POST", fmt.Sprintf("%s%s", c.APIBase, "/v1/payments/authorization/"+authID+"/reauthorize"), buf)
 	if err != nil {
 		return &Authorization{}, err
diff --git a/billing.go b/billing.go
index 5653411..877cd69 100644
--- a/billing.go
+++ b/billing.go
@@ -46,7 +46,7 @@ func (c *Client) CreateBillingPlan(plan BillingPlan) (*CreateBillingResp, error)
 // By default, a new plan is not activated
 // Endpoint: PATCH /v1/payments/billing-plans/
 func (c *Client) ActivatePlan(planID string) error {
-	buf := bytes.NewBuffer([]byte("[{\"op\":\"replace\",\"path\":\"/\",\"value\":{\"state\":\"ACTIVE\"}}]"))
+	buf := bytes.NewBuffer([]byte(`[{"op":"replace","path":"/","value":{"state":"ACTIVE"}}]`))
 	req, err := http.NewRequest("PATCH", fmt.Sprintf("%s%s", c.APIBase, "/v1/payments/billing-plans/"+planID), buf)
 	if err != nil {
 		return err
diff --git a/payment.go b/payment.go
index 8bd95ec..fe66071 100644
--- a/payment.go
+++ b/payment.go
@@ -22,10 +22,10 @@ type CreatePaymentResp struct {
 // CreatePayment is more common function for any kind of payment
 // Endpoint: POST /v1/payments/payment
 func (c *Client) CreateDirectPaypalPayment(amount Amount, redirectURI string, cancelURI string, description string) (*PaymentResponse, error) {
-	buf := bytes.NewBuffer([]byte("{\"intent\":\"sale\",\"payer\":{\"payment_method\":\"paypal\"}," +
-		"\"transactions\":[{\"amount\":{\"total\":\"" + amount.Total +
-		"\",\"currency\":\"" + amount.Currency + "\"},\"description\":\"" + description + "\"}],\"redirect_urls\":{\"return_url\":\"" +
-		redirectURI + "\",\"cancel_url\":\"" + cancelURI + "\"}}"))
+	buf := bytes.NewBuffer([]byte(`{"intent":"sale","payer":{"payment_method":"paypal"},` +
+		`"transactions":[{"amount":{"total":"` + amount.Total +
+		`","currency":"` + amount.Currency + `"},"description":"` + description + `"}],"redirect_urls":{"return_url":"` +
+		redirectURI + `","cancel_url":"` + cancelURI + `"}}`))
 	req, err := http.NewRequest("POST", fmt.Sprintf("%s%s", c.APIBase, "/v1/payments/payment"), buf)
 	if err != nil {
 		return &PaymentResponse{}, err
@@ -68,7 +68,7 @@ func (c *Client) CreatePayment(p Payment) (*CreatePaymentResp, error) {
 // ExecuteApprovedPayment - Use this call to execute (complete) a PayPal payment that has been approved by the payer. You can optionally update transaction information when executing the payment by passing in one or more transactions.
 // Endpoint: POST /v1/payments/payment/paymentID/execute
 func (c *Client) ExecuteApprovedPayment(paymentID string, payerID string) (*ExecuteResponse, error) {
-	buf := bytes.NewBuffer([]byte("{\"payer_id\":\"" + payerID + "\"}"))
+	buf := bytes.NewBuffer([]byte(`{"payer_id":"` + payerID + `"}`))
 	req, err := http.NewRequest("POST", fmt.Sprintf("%s%s", c.APIBase, "/v1/payments/payment/"+paymentID+"/execute"), buf)
 	if err != nil {
 		return &ExecuteResponse{}, err