WXOpenBusinessViewReq *req = [WXOpenBusinessViewReq object];
req.businessType = @"wxpayOverseaEntrustAuthorization"; // 固定值
req.query = @"sessionId=20211115171992080208"; // 20211115171992080208为预签约会话ID
req.extInfo = @"{\"miniProgramType\":0}"; // 固定值
[WXApi sendReq:req];

// 发起签约
int wxSdkVersion = api.getWXAppSupportAPI();
if (wxSdkVersion >= Build.OPEN_BUSINESS_VIEW_SDK_INT) {
WXOpenBusinessView.Req req = new WXOpenBusinessView.Req();
req.businessType = "wxpayOverseaEntrustAuthorization"; // 固定值
String SesssionId = "20211115171992080208"; // 预签约会话ID，通过下述预签约API获取
req.query = "sessionId=" + SesssionId; // 拼接参数
req.extInfo = "{\"miniProgramType\": 0}"; // 固定值
Boolean ret = api.sendReq(req);
} else {
// 微信版本太低，在这里提示用户升级后再完成签约
}

/********在WXEntryActivity的onResp里面接收签约结束回调，示例代码*******/
@Override
public void onResp(BaseResp r) {
if (r.getType() == ConstantsAPI.COMMAND_OPEN_BUSINESS_VIEW) {
WXOpenBusinessView.Resp launchMiniProgramResp = (WXOpenBusinessView.Resp) r;
String text = String.format("nextMsg=%snerrStr=%snbusinessType=%s",
resp.extMsg, resp.errStr, resp.businessType);
Toast.makeText(this, text, Toast.LENGTH_lONG).show();
// 对应时序图步骤3.4 - 3.6，调用查询签约API获取协议最新状态，然后更新商户侧签约状态
}
}